What process involves the sinking of oceanic crust beneath a deep-ocean trench?

The process of subduction is characterized by the sinking of denser oceanic crust beneath lighter continental or oceanic crust at a deep-ocean trench. This occurs at convergent plate boundaries where two tectonic plates collide. The oceanic plate, being denser and thinner than the continental plate, is forced down into the mantle, leading to a range of geological phenomena including the formation of trenches, volcanic arcs, and earthquakes.

This process plays a critical role in the recycling of Earth's materials, as the subducted oceanic crust eventually melts and contributes to magma formation, which can feed volcanoes. Subduction zones are essential for understanding mantle dynamics and the ongoing reshaping of the Earth's surface. In contrast, the other options—such as rifting, which involves the pulling apart of tectonic plates, and plate divergence, where plates move away from each other—do not involve the sinking of crust in the same manner. Crustal expansion generally refers to processes related to the creation of new crust rather than the destruction of it.